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Each part: 1 Mark
(a) A change in which one or more new substances are formed is called a chemical change. When steam is condensed, it becomes water. Only the state of $H_{2}O$ changes. A new substance is not formed. So, it is not a chemical change.
(b)When two liquids are immiscible and are taken together in a funnel, the heavier liquid forms the bottom layer and the lighter liquid forms the top layer.

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(a) Characteristics: 2 Marks
(b) Explanation: 1 Mark
(a) The characteristics of chemical changes are:
1) It is a permanent change and is irreversible.
2) New substances are formed in this change.
3) Energy in the form of heat or light is either absorbed or released.
(b)When wood is lit up, it burns gently and after a while, it turns into ashes. As it burns, it produces heat, light and smoke which escapes through the chimney. The heat, light, fire and smoke are all good characteristics of a chemical reaction, which result in a completely new matter—ash.

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Definition: 1 Mark
Factors: 0.5 Mark each
Corrosionis a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment.
Thefactors which affect corrosion are:
1. More the reactivity of themetal,more will be the possibility of the metal getting corroded.
2. Presence of carbon dioxide in natural water increases rusting of iron.
3. When the iron surface is coated with layers of metals more active than iron, then the rate of corrosion is retarded.
4. A rise in temperature (within a reasonable limit) increases the rate of corrosion.

Answer: Option A. ->
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Physical and chemical change: [0.5 Marks each]
1) Photosynthesis and burning of coal $\to$ Chemical change.

2) Dissolving sugar in water and melting of wax $\to$ Physical change.

Answer: Option A. ->
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Definition: 1 Mark each.
1) The process of deposition of a layer of zinc on iron is called galvanization. It prevents direct contact of iron with air and oxygen.

2) The process of formation of solid crystals from a homogeneous solution is called crystallization and it is a physical change. Eg: Formation of copper sulphate crystals.

Answer: Option A. ->
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Correct Answer: 0.5 Mark each
The breaking of a pencil lead: It is a physical change as no new substance is formed.
 
Tarnishing of silver: It is a chemical change as rust is formed in it.
Digestion of food: It is a chemical change as new substances are formed.
Melting of an Ice cube: It is a physical change as only the change of state takes place.

Answer: Option A. ->
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Change: 1 Mark
Justification: 2 Marks
Blending a smoothie involves two physical changes: the change in shape of each fruit and the mixing together of many different pieces of fruit. There is no chemical change in the process.
This is a physical change because blending does not cause the fruits to become a fundamentally different substance. A new substance is not formed. It is a mixture of substances. So, it is a physical change.

Answer: Option A. ->
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Each part: 1 Mark
1) Sodium hydrogen carbonate is the chemical name of baking soda.
2) When vinegar reacts with baking soda, carbon dioxide is formed.
Vinegar (Acetic acid) + Baking soda (Sodium hydrogen carbonate) → Carbon dioxide + other substances
We can say that the above reaction is a chemical change because carbon dioxide is formed. It is a new substance.
 

Answer: Option A. ->
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Changes: 1 Mark
Explanation: 2 Marks
When a candle is burnt, two types of changes occur
i) Physical Change
ii) Chemical Change
When the candle is lit, the wax at the top melts. This is a physical change.
The wick absorbs liquid wax. The liquid wax vaporizes due to the heat produced by the flame. This wax vapour near to flame burns and gives new substances like Carbon Dioxide, Carbon soot, water vapour, heat, and light. This is an irreversible change.

Answer: Option A. ->
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(a) Products: 1 Mark 
     Equation: 1 Mark
(b) Explanation: 1 Mark
(a) When a magnesium ribbon is burnt, magnesium oxide is formed. The equation for the reaction is given below.
$Mg+O_2\to MgO$
When magnesium oxide is dissolved in water, magnesium hydroxide is formed. The equation for the reaction is as follow:

$MgO+H_{2}O\to Mg(OH{)}_2$
(b) When wood is burnt, a new substance is formed. Therefore, it is a chemical change. However, when we cut wood, only the shape and size of the wood changes but no new substance is formed. Therefore, it is a physical change.